The present invention generally relates to electronic data communication systems. More particularly, the invention relates to methods and apparatus for transmitting information between a central site and multiple electronic data subscribers.
The advent of Internet service and video communication, among other advances associated with the transmission of electronic data, has generated an increased consumer desire for electronic data transfer to and from an equipment terminal such as a computer, a television, or the like. This increased desire has generated an increased demand for communication providers, such as telephone companies and Internet service providers, to handle increasing amounts of data.
Typical communication systems include existing telephone infrastructures such as the public switched telephone network (PSTN) to transfer both telephone service (e.g., voice band data) and electronic data (e.g., video with or without accompanying audio and/or internet information) to and from a telephone or terminal. Using an existing telephone network infrastructure to transfer data to and from a terminal allows communication providers such as telephone companies to leverage their existing telephone connections to households for both voice and data transfer. In particular, existing PSTN phone lines, typically twisted-pair wires, between a subscriber and a central site such as a central office of a PSTN may be used to transmit both telephone service (voice) and electronic data. The twisted-pair wires may transmit data at frequency bandwidths ranging up to several MHZ; however, the PSTN generally includes filters and data sampling apparatus that limit voice frequency bandwidth to about 3 kHz. Consequently, data transfer over the PSTN is also generally limited to a bandwidth of about 3 kHz, absent modifications to the PSTN.
Digital subscriber line (xDSL) communication systems, which may include asymmetric digital subscriber line, symmetric digital subscriber line, high-speed digital subscriber line, very high-speed digital subscriber line, or other digital subscriber line technologies, and the like, may be used to transmit information over twisted-pair wires at a greater bandwidth; e.g., up to several MHZ by bypassing the voice frequency digital sampling apparatus and at least some of the PSTN filters. The xDSL systems generally include a subscriber modem attached to a subscriber terminal and a corresponding system modem located within or proximate a central office of the PSTN or a similar central site within the telephone system. The system modem typically includes an analog-to-digital converter, a digital-to-analog converter, and a bit pump to convert electronic information into an appropriate format for transmission over PSTN lines.
Because space requirements and power consumption at the central office increase with each additional modem in the central office, it is desirable to minimize or reduce the number of modems at the central office. Also, data transmitted over communication lines typically occurs in bursts; i.e., the data is not always transmitted in a continuous stream. Hence, the central office is theoretically able to provide data transfer service to a number of subscribers that exceeds the actual number of modems resident at the central office. In other words, it may provide oversubscription of data transfer services.
An xDSL system that allows oversubscription of consumer modems to a central office is disclosed in U.S. Pat. No. 5,668,857, issued Sep. 16, 1997 to McHale. The system disclosed in the McHale patent includes a communication server, located within a central office of a PSTN, which includes a switch, a modem pool, and a controller connected to both the switch and the modem pool. The controller polls the subscribers or a subset thereof and determines whether a particular xe2x80x9cpolledxe2x80x9d subscriber is attempting to send data to the central office. If an attempt is detected, the controller directs the switch to couple the subscriber transfer line to a selected subset of modems in the modem pool. The switch disclosed in the McHale patent is an analog device; i.e., the format of the signal is analog on both the input and output data lines connected to the switch. An output signal from the switch is transferred to the system modem, which converts the signal from an analog format to a digital format.
Analog switching of data lines connected to modems may be inadequate in several regards. For example, analog switching may be inefficient because, in part, when data is transmitted to a subscriber modem, time is required to determine which system modem will connect to the subscriber modem, and time is required to establish the connection. Systems employing analog switching techniques may require additional system modems located within or near the central office to overcome the time requirements for modem selection and switching.
Additional problems with using analog switches include the generation of transients in a circuit as the circuit is switched. Additionally, analog switching may be unreliable and require significant board space at the central office. For these reasons and others, analog switching of data communication lines causes transmission quality problems and may be relatively expensive. Therefore, improved methods and apparatus are desirable for efficiently handling multiple data transmission subscribers.
The system disclosed in the McHale patent uses polling devices and techniques to determine when and if a subscriber modem is attempting to send payload information to the communication server. The polling device polls subscriber modems (one at a time) that may be attempting to send information to the server. The polling circuitry of the device dwells on each subscriber line for a period of time sufficient to allow the polling device to determine whether the corresponding subscriber modem is ready to transfer information to the server. The subscriber modem may indicate readiness by continuously or repeatedly sending ready signals to the system modem until the system modem acknowledges the ready signal. If, during the dwell period, a modem sends a signal indicating that the modem is ready to transfer information to the communication server, the subscriber modem is connected to a communication server modem. No subscriber can send any payload information to the server until the polling circuitry is coupled to the particular subscriber modem. Although this polling technique allows oversubscription of subscriber modems relative to the server modem, this technique is relatively inefficient because, among other reasons, subscriber modems must wait until the modem is polled to send payload information to the communication server. Thus, only one subscriber modem coupled to the polling device may send payload information to the server at any one time. The remaining modems coupled to the polling device must wait until polled to send payload information to the server, resulting in relatively inefficient use of the system modem. Therefore, improved methods and apparatus for efficiently handling multiple data transmission subscribers are desirable.
The present invention provides improved method and apparatus for transmitting voice and electronic data over a data communication system. The way in which the present invention addresses the drawbacks of the now-known data communication systems and components thereof is described in greater detail hereinbelow; however, in general, in accordance with various aspects of the present invention, the inventive apparatus provides an improved communication system with a fewer number of system data pumps than a number of subscribers desiring data communication capability. In addition, the inventive system is configured such that the system does not require analog switching to connect subscribers to the data pumps. Thus, unwanted problems such as time delay and switching transients associated with analog switching methods and apparatus are reduced. Furthermore, the system is configured to allow subscribers to send a predetermined amount of information toward the data pump on demand (without first being polled by the system data pump).
In accordance with an exemplary embodiment of the present invention, the communication system includes a number of data converters configured to transform data between a form suitable for transmission between the subscriber modems and the converters and a form suitable for the data pump. In accordance with a further aspect of this embodiment, a plurality of data converters are coupled to a single data pump.
In accordance with another embodiment of the present invention, each data converter includes an analog front end configured to communicate with the subscriber modem or terminal, an analog-to-digital converter, and a digital-to-analog converter.
In accordance with yet another embodiment of the present invention, the system includes buffer memory interposed between the data converter and the data pump. The buffer memory is configured to store a fixed amount of information until the data pump is ready to receive the information. The buffer memory allows subscribers to send a fixed amount of information to the buffer without waiting for availability of or acknowledgment from the system data pump. In accordance with this embodiment, a predetermined maximum amount of information can be sent from the subscriber modem to the corresponding buffer memory without the subscriber modem receiving an acknowledgment signal from the data pump and without the subscriber modem being polled. This allows more efficient transmission of data between subscribers and a central site.
In accordance with another embodiment of the present invention, the data pump broadcasts downstream data to all subscriber modems or terminals attached to the data pump. The downstream data includes information to identify the subscriber modem or terminal which is to convert and decode the data for a particular subscriber""s use. In addition, the downstream data includes information that allows all modems coupled to the data pump to maintain synchronization with the pump. In accordance with a further aspect of this embodiment, the downstream data includes an acknowledgment that indicates to the subscriber modem that the subscriber modem may send additional information.
In accordance with a further embodiment of the present invention, information transmitted from a subscriber to a corresponding data converter includes information that allows the subscriber modem and the data pump to restore synchronization.
In accordance with yet another embodiment of the present invention, electronic information is transmitted over a communication system from a subscriber modem to a system splitter that is located at a central site. The information is filtered into a low frequency bandwidth and a high frequency bandwidth. The high frequency bandwidth data is transmitted to a system converter and converted at the converter into digital format. The digital information is transmitted to a storage buffer, and then transmitted to a system data pump.